Cathode ray tube having spiral acceleration anode



30, 1966 K. SCHAFFERNICHT ETAL. 3,270,234

CATHODE RAY TUBE HAVING SPIRAL ACCELERATION ANODE Filed July 22, 1960 INVENTORS Klaus Schclffernichr 8:

Gunther Knube BY I ATTORNEY United States Patent 3,270,234 CATHODE RAY TUBE HAVING SPIRAL ACCELERATION ANODE Klaus Schaifernicht, Ulm (Danube), and Giinther Knabe,

Pfuhl, Germany, assignors to Telefunken Aktiengesellschaft, Berlin, Germany Filed July 22, 1960, Ser. No. 44,726 Claims priority, application Germany, July 30, 1959,

1 Claim. (Cl. 31383) The present invention relates to a cathode ray tube having two pairs of opposed deflection plates which are arranged one behind the other in the axial direction of the beam of the tube, which tube also has electrode means for producing an after acceleration field.

It is generally customary to provide cathode ray tubes having electrostatic deflection means with an after accelerating field. This after accelerating field is usually produced by means of an electrode which is deposited on the inner surface of the tube envelope. A known type of after acceleration electrode consists of a spiral resistance coating applied on the inside of the conical portion of the tube envelope. With such known arrangements, the after accelerating field reaches into the zone between the deflection plates and particularly into the zone between those plates which are nearer the screen, hereinafter referred to as the screen-side plates.

Inasmuch as it is generally desired to make such tubes as short as possible, every attempt is made to place the screen-side deflection plates as close as possible to the conical part of the cathode ray tube envelope, or even to let these deflection plates extend into the conical portion of the tube. In such tubes, the distance between the defiection mid-point of the deflection plates and the start of the spiral accelerating anode is very critical, especially where the after accelerating electrode starts well within the conical portion of the cathode ray tube envelope so that the electric field 6 changes rapidly in the axial direction. As a result, the effect produced by the after acceleration field which interacts especially with the screen-side pair of deflection plates is to a large extent dependent on the axial distance of the screen-side deflection plates from the start of the after accelerating electrode. This distance must therefore be maintained very exact, and this renders the construction of such a cathode ray tube unduly complicated and expensive.

It is, therefore, an object of the present invention to provide a cathode ray tube which overcomes the above disadvantages, and which is less sensitive to variations in accelerating anode potential.

More particularly, it is an object of the present invention to provide a cathode ray tube having an after accelerating anode and pairs of deflection plates, wherein the axial distance between the screen-side deflection plates and the beginning of the after accelerating anode is no longer critical, so that manufacturing tolerances can be relaxed.

With the above objects in view, the present invention resides mainly in a cathode ray tube of the above-described type in which the accelerating anode is so arranged and constructed that the after accelerating field g in the region of the screen-side deflection plates is axially substantially homogeneous, i.e., that n I 0 52 where g is the electric field 6V namely,

and z is the axis of the tube.

Patented August 30, 1966 Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

The single figure is a diagrammatic illustration of an embodiment of the invention employing a spiral accelerating anode of constant pitch.

Referring now to the drawing, the figure shows a cathode ray tube having a tubular neck portion I joined to a conical portion 2 of the vacuum envelope. Of the entire deflection system, only the screen-side deflection plates .3 and 4 are illustrated. In the instant embodiment, the screen-side deflection plates 3 and 4 are located entirely within the tubular neck portion 1. The after accelerating field is produced by a resistance spiral 5 which is on the inner surface of the envelope. The end of the spiral which is near the cathode is connected with a coating 6 which is coextensive in the axial direction with the screen-side deflection plates 3 and 4.

Of particular importance is the fact that a portion of the after accelerating spiral coating 5 extends into the tubular neck portion 1 of the tube, which tubular neck portion, in this case, has a constant diameter, and that the screen-side deflection plates 3 and 4 are located in this tubular neck portion and are arranged to approach each other somewhat in a direction toward the cathode 9. Inasmuch as in the instant embodiment the after accelerating electrode has the same resistance per unit length, the last turns of the after accelerating spirals which extend into the tubular portion produce in the region of the screen-side deflection plates a substantially homogeneous after accelerating field.

The advantage of the arrangement according to the present invention is that the axial location of the deflection plates is far less critical than in cathode ray tubes in which the after accelerating anode does not extend into the tubular portion of the tube occupied by the detflection plates. This is explained by the fact that the after accelerating field in the immediate vicinity of the screen-side deflection plates is substantially homogeneous, so that the interaction of the after accelerating field with these plates is constant in the vicinity thereof. Expressed mathematically, the accelerating field 6; which itself is the first derivative of the voltage V with respect to the tube axis 2 or 6V F5 is constant, which means that field gradient, which is the first derivative of the field namely,

is equal to 0.

A further advantage of the present invention is that the distortion of screen-side deflection plates is substantially independent of the ratio between the total acceleration voltage and the anode voltage. Furthermore, in a cathode ray tube according to the present invention, pattern correction has hardly any eifect on the distortion of the cathode-side deflection plates, so that it is now possible to correct the distortion of the screen-side deflection plates by varying the voltage between the end of the after accelerating spiral which is nearer the cathode and the mean deflection plate potential, without simultaneously affecting the distortion of the cathode-side deflection plates.

The homogeneity of the field can be achieved either by so fashioning the spiral that its resistance decreases per unit length, or by increasing the pitch of the spiral in the direction toward the screen. In either case, the axially directed electric field remains homogeneous.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claim.

We claim:

A cathode ray tube having a cathode and a screen, comprising, in combination:

4 inner surface of said envelope, such that said electrode is a means for producing in the region of said screen-side deflection plates, an after acceleration field which, considered in the direction of the beam,

(a) an envelope having a tubular neck portion of substantially constant diameter and a flaring conical portion joining said neck portion;

(b) at least two pairs of deflection plates located between the cathode and screen, said pairs being arranged one after the other with respect to the di rection of the beam emanating from the cathode so that the plates of one of said pairs constitute screenside deflection plates, said screen-side deflection plates being located entirely within said neck portion; and

(c) an electrode for producing an after acceleration field between said screen-side deflection plates and the screen, said electrode consisting of a conductive coating applied to the inner surface of said envelope and located partly in said conical portion and partly in said neck portion, said coating being in the shape of a spiral of changing pitch and being made of a material having substantially the same resistance per unit length, the distribution of said coating being, in dependence on the configuration of said 5 is substantially homogeneous, i.e.,

where "is the electric field and z is the distance measured along the axis of said envelope.

References Cited by the Examiner UNITED STATES PATENTS 2,088,493 7/ 1937 Sutherlin et a1 31|3--78 2,096,415 -9/ 1937 Weinhart 3 1378 2,119,559 -6/ 1938 Ronei 31 378 2,123,636 7/1938 Schwartz 31-378 2,986,668 5/1961 Haflinger et al. 313--83 X FOREIGN PATENTS 735,463 8/ 1955 Great Britain.

DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON, GEORGE WESTBY, Examiners.

R. SEGAL, D. E, SRAGOW, Assistant Examiners. 

